The present invention relates to a compensating device suitable for use in railway car transformers having at least one compensation receptacle. The compensation receptacle has a fluid-carrying connection with the interior of the housing of the transformer, carries a fluid volume, and has a separating element limiting the fluid volume in the compensation receptacle. The separating element is in the form of a membrane having a circumferential border connected with and sealed to the side walls of the compensation receptacle at some distance form its bottom. With modification of the fluid volume in the compensation receptacles, the separating element is subject to modification of its position.
Work temperatures of from xe2x88x9230 degrees C. to 135 degrees C. prevail during the operation of transformers in railway cars. The fluid used as transformer fluid, generally in the form of silicon oil, is subject to volume fluctuations of greater than 10%. In order to be able to compensate for these temperature-dependent volume fluctuations, a compensation receptacle is conventionally provided which can store transformer fluid and can deliver the transformer fluid through a fluid-carrying connection into the interior of the housing of the transformer when low operation temperatures prevail. During operation at high temperatures, it can carry transformer fluid out of the housing of the transformer.
In order to be able to fulfill this function, one compensation receptacle is disclosed in EP 0 743 661 A3. A vertically movable guided compensating plate is arranged in the compensation receptacle. The plate serves as a separating element, separating the fluid volume of different magnitudes in the compensating receptacle form the ambient atmosphere. To guide the movement of the compensating plate, two sheathings are provided in the compensation receptacle which slide relative to one another. One sheathing is fastened to remain stationary. The other sheathing is fastened to the compensating plate. A spring arrangement located within the sheathing produces a prestressing or servo-force, seeking to move the compensating plate in the direction corresponding to the diminution of volume.
This device of EP 0 743 661 A3 is costly to manufacture, and is of complicated construction which is a considerable disadvantage. Since transverse acceleration in the magnitude of 5 g can occur with the use of such compensating devices in transformers for the operation of railway cars, the sheathing and spring arrangement, in the compensation receptacle forming the movable positioning of the compensation plate, must be manufactured very carefully. Construction is costly, if the predetermined tolerances are to be maintained to avoid disruptions of operation when transverse acceleration occurs. On the other hand, the location of the sheathing and spring arrangement in the interior of the compensation receptacle leads to a dead space of considerable volume, because the guiding obtained by the sheathings moving relative to one another allows for only a limited length of passage for the movement of the compensating plate. As a result, a very unfavorable ratio results between structural dimensions of the compensation receptacle and magnitudes of variable fluid volume remaining available as compensation space.
A compensating device disclosed in U.S. Pat. No. 4,609,900 is suitable for use with small-format, high voltage transformers, and provides a membrane as separating element. The separating element is guided by means of a spring-biased guide member within the compensation receptacle. In the position corresponding to the smallest volume of fluid, the membrane extends into the intermediate space between the container interior wall and the guide member against the bottom of the compensation receptacle. With wave movements of the guiding member occurring counter to the spring force form the bottom, the non-expandable membrane is laid out in the intermediate space between the receptacle interior wall and guide member in an unrolling folding over upon itself. Also, with this compensating device of this type, a very unfavorable ratio exists between structural dimensions and the volume remaining available as compensation space. Additionally, the use of a spring-biased guide member guided on the housing leads to a complicated and costly construction.
Objects of the present invention are to provide a compensation receptacle which can be manufactured of simpler construction and at low cost, and which is characterized by an improved ratio between structural dimensions and variable compensation volumes. In a compensating device, these objects according to the present invention are attained in that a roll-over membrane having waves is provided as the membrane. The membrane can be rolled out with pulling flat of the waves. Correspondingly, in its rolled-up state, the membrane extends in a position freeing the greatest volume of fluid, essentially in a plane at some distance form the bottom.
According to the present invention, utilization of a roll-over membrane as separating element on the one hand facilitates particularly simple construction and correspondingly greatly decreased manufacturing costs for the compensation receptacle. On the other hand, it provides the advantage that nearly the entire volume of the compensation receptacle, without having a dead space volume present and without dropping in weight, is available as variable compensation volume. This is attained in that the roll-over membrane is of such dimensions that it extends in rolled-up state practically in a plane in which it frees essentially the entire interior space of the compensation receptacle for the fluid volume, and that it can be unrolled out of this position into a trough-like or cup-like configuration in which it is closely adjacent to the interior surface of the compensation receptacle, in other words to the bottom and the side walls. Thus, an especially good ratio between structural dimensions of the compensation receptacle and dimensions of usable compensation volume is attained.
A compensation device disclosed in CH-A-436 368 has a membrane as a separating element, which is not expandable. The membrane is of a metal foil, on both sides of which is applied a plastic foil. The missing expandability of the membrane prevents it from extending to the position corresponding to the greatest fluid volume in a plane at some distance from the bottom. This device is much rather configured as a spherical vessel in which the membrane is hollowed out convexly or concavely in a trough-like manner.
Another particular advantage of the compensation device according to the present invention involves using compensation receptacles, produced in a simple and low-cost method of construction, for the operation of the relevant transformer by a plurality of quite small-volume compensation receptacles provided in a modular arrangement. When using a plurality of small-volume compensation receptacles constructed together in modular construction to form a modular compensation device associated with a transformer, the disturbing influence of the sloshing of the transformer fluid in the compensation receptacle, as it occurs in conventional compensation devices, is reduced. With the conventional devices, measures must be taken in order to suppress the destructive influences of the sloshing occurring with the presence of transverse acceleration caused by the springing expansion working on the movable compensation plate, which presses the compensation plate on the fluid surface. With the present invention, on account of its subdivision of the compensation arrangement into a plurality of small partial volumes, no measures for the suppression of the sloshing effects are required. Thus, it is not required that the roll-over membrane represent a stabilizing element to counter the sloshing. The surface of the roll-over membrane without any further difficulty can be of such dimensions that even in an entirely rolled-out state, it corresponds to the smallest fluid volume, having dimensions which are only slightly smaller than the interior surface of the compensation receptacle defining the fluid volume. The roll-over membrane, even in the state of the smallest fluid volume (in other words in completely rolled-out state), stands under only a slight tensile stress.
The modular construction of the compensating device made up of a plurality of compensation receptacles arranged on the transformer housing permits suitable grouping of the compensation receptacles. Free spaces on the top surface of the transformer housing can then be used for cable through-conductance or the like.